Electronics are engulfing every discipline of human life, the reverberation of which is found in consistent research to develop improved products. Broadly, while the research is focussing on the physiology of the electronic gadgets to make it more enduring with additional loads, anatomically they are being made compact. The constant endeavour to achieve the said progression has been invariably through new materials and methods.
In the discipline of optoelectronics, the thrust to develop an alternate to the expensive and brittle Indium-tin-oxide (ITO) is increasing. Indium-tin-oxide has been the cynosure of the organic light emitting diodes, solar cells and the like because of the unique combination of the advantage it offers over the other materials like high electrical conductivity and optical transparency. Indium oxide optimally doped with tin is unique in this respect. It retains its optical band gap (˜4 eV) yet exhibits high conductance arising because of tin donating electrons to the conduction band (Kim, H. et al; J. Appl. Phys. 86, 6451-6461, 1999). A good ITO film can transmit up to ˜92% of visible light and show a sheet resistance (Rs) of ˜11 Ω/square which explains its widespread use as electrode material in display devices.
Alternatives to ITO such as fluorine doped tin oxide (FTO), (Rakhshani, A. E. et al; J. Appl. Phys. 83, 1049-1057, 1998; Nunes, P. et al; Vacuum 64, 281-285, 2002) and other oxide systems (Edwards, P. P. et al; Dalton Trans. 19, 2995-3002, 2004; Gordon, R. G. MRS Bull. 25, 52-57, 2000), have been explored but their performance has been found to suit only certain applications. Further oxides are poor IR and UV transmitters and are brittle, not suitable for flexible applications.
An attractive alternate to ITO is graphene (Geim, A. K. et al; Nat. Mater. 6, 183-191, 2007). However, obtaining extended layers of graphene can be process intensive and cost forbidding (Bae, S. et al; Nat. Nanotechnol. 5, 574-578, 2010). The organic equivalent to ITO is poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives, but they suffer from limited conductivity and stability besides being expensive (Girtan, M. et al; Sol. Energ. Mat. Sol. 94, 446-450, 2010).
Fabricated devices like transistors, gas sensors, solar cells, IR detectors comprise suitably patterned materials for their application. Patterning of materials with wires of different dimensions, millimetre to submicrometer is of immense interest owing to their unusual properties that can be harnessed by their appropriate usage in various devices.
Cracks or discontinuations in bodies are one of the undesired manifestations of the stress induced through the surface of the bodies. The cracks are a common phenomenon in paintings, wall surfaces and mud surface. Cracks which initially give an awkward appearance to the body in which it has developed, can be ruinous if left unattended. Substantial research has been carried out to understand the factors, which initiate and propagate cracks. The research has pointed to various factors like particle size, temperature, solvents, rate of drying, magnitude of stress, crystallographic orientation of substrates (Nam, K. H. et al; Nature 485, 221-224, 2012).
While the major research on cracks is oriented towards understanding and implementing the factors which can resist them, studies to exploit the cracks for various advantages including deposition of metals have not yielded appreciable results. The main reason being lameness to identify a material which can crack (more specifically crackle wherein the substrate at the bottom is exposed) or a method which renders a material to crackle in accordance with the specific need and on a large area. To be precise, material/method that is easy to adopt in the patterning of various substrates with different materials.
The literature provides information wherein different materials are induced to crack by stress through a micro notch created by ion beam etching and terminated at the free end of the sacrificial film. The prior art process are limited as they can be applied to specific substrates such as Si<110> and <100> with usage of sophisticated instruments. Further, large area is difficult to be patterned because of serial and multistep processes; known processes have been successful in patterning an area of about micrometer square regions. The etching of cracked layer requires expensive and corrosive chemicals, also the possibility of the etched layer for recycling is remote. Another major disadvantage has been discontinuation in cracks without interconnection and the dimensions of the cracks being uncontrollable. The processes take long time for patterning and fabrication.
The present disclosure targets to provide solution at two different levels. Primarily to overcome the drawbacks/difficulties associated with the formation of crackles suitable for their usage as templates in patterning of micro and submicrometer dimensional wires of apposite materials on various substrates. Secondly, by the usage of the aforesaid patterned substrates with micro and submicrometer wires in the fabrication of various devices of electronics discipline to overcome the difficulties associated with the usage of various oxides including ITO.
The present disclosure provides a composition, which crackles when applied as thin films on various substrates and convenient to lift off. The crackles are used as templates to dope with various materials including conducting materials, semiconducting materials, insulators, dielectrics and energy, thus patterning the substrate with micro and submicrometer dimensional wires for appropriate usage in various electronic/optoelectronic devices.